The present invention relates to an electrorheological liquid or, more particularly, to an electrorheological liquid having excellent uniformity and durability to be suitable for use in a wide temperature range from low to high temperatures and exhibiting controllability of viscosity not only by means of adjustment of electric field applied thereto but also by means of temperature adjustment.
An electrorheological fluid, hereinafter referred to as an ER fluid, is a liquid having a relatively high flowability at an ordinary state and imparted with a greatly increased viscosity when placed in a direct-current electric field so that it is highlighted in recent years as a novel functional material. ER fluids of the most conventional class include a suspension of fine colloidal particles such as zeolites in an electrically insulating liquid such as silicone oils.
Although such an ER fluid based on a dispersion of colloidal particles exhibits a large electrorheological effect or, namely, a large increase in the viscosity by the application of an electric field, a problem in such an ER fluid is that settling or agglomeration of the colloidal particles sometimes takes place in the fluid to cause troubles in the practical use of the fluid.
It is known that some of organic thermotropic low-molecular liquid crystal compounds exhibit an electrorheological effect and have a possibility of application as an ER fluid. Although these ER fluids have no problems in respect of the homogeneity, they have an unavoidable limitation in the increment of the viscosity by the application of a direct-current electric field as an inherency in a low-molecular compound. It is also a possible idea to employ a lyotropic polymeric liquid crystal compound dissolved in an organic solvent as an ER fluid. Such a solution-type ER fluid has a problem in respect of the stability and durability as a consequence of evaporation of the solvent or by the absorption of moisture from the atmospheric air.
Under these circumstances, it is eagerly desired to develop an ER fluid having excellent homogeneity and durability and capable of exhibiting a large electrorheological effect.